You may have had enough on this topic, but I'll add a quick note and a
photo. Here on the coast (White Rock, BC), where it hardly ever gets
bitter cold, we find that a Christmas light (incandescent, of course)
gives off enough heat to keep HB nectar from freezing. We leave the
feeder out all night, and it has done fine for the last 10 days or so of
slightly sub-freezing weather (never below 20° F.) We've had an Anna's
coming very regularly for about 3 weeks. There's a link to a photo
below (not crystal clear, unfortunately--it's shot through double paned
glass).